Flow vortices inside the magnetopause associated with FTEs moving along the magnetopause

On the low-latitude dayside magnetopause, the magnetic field signatures of FTEs, identified from bipolar variations in the normal components, appear to vary with distance from the magnetopause. If spacecraft takes a trajectory which remains in the magnetosheath and just grazes the sheath-side of the moving FTE structures, it will register a peak in the field magnitude typically accompanied by a decrease in the number density compared with the background sheath. If spacecraft is very close to the magnetopause, it may observe two dips in the field magnitude just adjacent to the bipolar normal component perturbations or observe a single dip right at the center of the bipolar structure, and these different signatures can be interpreted as evidence that FTEs moving along the magnetopause locally displace the magnetopause into the magnetosphere and they are embedded inside these kinks. Plasma flows on these two kinds of trajectories show bipolar perturbations in the normal direction with negative followed by positive; the tangential flow is generally along the sheath flow direction. When spacecraft is located within the magnetosphere, it may record enhancements of field strength and increases in the number density. The flow perturbations in the normal direction still can be observed. The tangential flow can be either along or against the background sheath flow depending on whether spacecraft is close to or distant from the magnetopause in the magnetosphere. This flow pattern has the form of a flow vortex just inside the magnetopause associated with the FTE moving outside the magnetopause. These flows around FTEs are relevant to their interactions with the magnetosphere, and viscosity may play an important role here. In addition, the momentum transport between FTEs and the magnetosphere suggests that in most cases FTEs can not be in a force-free state.